The era of this movie takes place is before my time, but learning this is supposed to be based on a true story, I'm quite sure both parties had to make adjustments to their preconceived opinions each had toward one another, beginning with their initial meeting and throughout the tour destinations.
When I first saw the Imperial, it was parked in front of the 2 Cadillac's just as they were preparing to start the tour. The 2nd time was by a restaurant, and as you mentioned, it was slightly blurred and in the background. I thought the music agents were going to meet them at the restaurant, or something, but the Imp was just there for the scene as a period correct car.